type IsUndefined<T> = T & undefined extends never ? false : true;
/**
 * UndefinedAsOptional marks all properties that can be `undefined` as optional
 *
 * @example
 * type Foo = {
 *   a: string
 *   b: number | undefined
 * }
 * type Bar = UndefinedAsOptional<Foo>
 *
 * // Bar is equivalent to:
 * type Bar = {
 *   a: string
 *   b?: number
 * }
 *
 * const x: Foo = { a: 'foo' } // Error: Property 'b' is missing in type '{ a: string; }' but required in type 'Foo'
 * const y: Bar = { a: 'foo' } // OK
 **/
export type UndefinedAsOptional<T> = {
    [K in keyof T as IsUndefined<T[K]> extends false ? K : never]: T[K];
} & {
    [K in keyof T as IsUndefined<T[K]> extends true ? K : never]?: T[K];
};
export {};